They sell little tiny pebbly bits of stuff (cork maybe) that will give you a rocky desert look. That might be cool.
I put a thick coat of brown paint down anf sprinkle the base material (genrally flock in my case) onto the wet paint so it dries in. I like this method for flock since you don’t paint flock. I bet some glue (even maybe just white Elmers) would work wel for pebbly stuff to be painted.
If you have a spare base try it on eone of them and see what you get.